There does not seem to be a way to set the <jsp-config> properties using the web.xml editor tab:
<jsp-config>
<property name="keepgenerated" value="true">
<description>Keep a copy of the generated servlet class' java code.</description>
</property>
</jsp-config>
Thanks
Leonid

Yes, enhancement.
This is a feature we had in the old editor before we migrated to multiview, but the 6.0 schedule was too tight to
complete it and there hasn't been time since then. It's really useful though, so we should really try to get this into 7.0.